Wind tunnels are used in aerodynamic research to study the effects of air moving past solid objects. A wind tunnel can generally consist of a passage with the object under test disposed and/or mounted therein. Air is made to move past the object by a fan system or other means. The test object, sometimes called a wind tunnel model, can be provided with instruments having suitable sensors to measure aerodynamic forces, pressure distribution, or other aerodynamic-related characteristics observed by the test object.
Referring to FIG. 1, in the world of consumer products, such as paper toweling, bath tissue products, and facial tissue products, wind tunnel 10 tests can be used to suitably measure simulated air velocities, forces, and/or pressures exerted upon a web material 18 while the web material 18 is conveyed from one location to another. Such conveying is known to those of skill in the art as converting.
Referring to the exemplary prior art wind tunnel 10 of FIGS. 1 and 2, air 32 (or airstream 32) is blown or sucked through a duct equipped with instrumentation where an object (here presented as web material test stand 12) is positioned for study. Typically the air 32 is moved through the wind tunnel 10 using a wind generating device 14 in the form of a fan 30. For very large wind tunnels that are several meters in diameter, a single large fan may not be practical, and so instead an array of multiple fans 30 can be used in parallel to provide sufficient air flow through the wind tunnel 10.
In a typical web material 18 wind tunnel 10 set-ups, a test stand 12 can provide for a web material 18 to be attached to a web material support 16. The web material support 16 will typically be provided as a roller, turn bar, or the like having a nominal diameter, or Z-direction thickness, D. In most applications, the web material support 16 will be provided to represent typical web material 18 handling equipment used in the production of consumer products such as paper toweling, bath tissue, facial tissue, as well as web materials 18 suitable for the production of assembled articles such as diapers, catamenial devices, and the like.
During wind tunnel testing of web materials 18, any turbulence 34 present in air 32 has a deleterious effect upon the analysis of the web material 18 disposed upon test stand 12. Thus, in order to suitably test web materials 18 disposed upon test stand 12 it is preferred that the air 32 moving through the wind tunnel 10 be relatively turbulence-free and laminar.
Web materials 18, including web materials 18 having high surface texturing, such as unusual or complicated shapes are generally analyzed in wind tunnels 10 in order to understand boundary layer air (i.e., air located proximate to web material 18). Such testing can provide the necessary design analysis to help in the development of equipment for the handling of web materials 18, especially web materials 18 that preferably move at high rates of speed during converting operations.
However, it is a common problem experienced by those of skill in the art that the air 32 provided by the wind generating device 14 becomes turbulent 34 upon contact with the relatively blunt leading edge surface of web material support 16. This turbulent air 32 negatively impacts the analysis of web materials 18. This includes those web materials 18 having high surface texturing.
Another issue that can arise with such test stands 10 as described supra, is the effect of the application of a tension, T, to the web material 18 attached to the test stand 10. One of skill in the art will understand that typical web materials 18 used in the production of the articles mentioned supra are typically subjected to high tensions in order to secure the most efficacious winding, effect a complimentary registration of the web material 18 relative to a particular portion of the manufacturing operation, or even the registration of one web material 18 to another web material 18. Applying a tension to the web material 18 disposed upon the test stand 10 assists the analysis of the web material in conditions that more accurately simulate actual manufacturing conditions.
To note, it should be readily understood that web materials 18 used in the production of paper toweling, bath tissue, or facial tissue are typically thin (e.g., have a caliper ranging from about 0.005 inches to about 0.020 inches) and have a very low basis weight (e.g., about 5 pounds/3,000 ft2 to about 30 pounds/3,000 ft2). In other words, the web materials 18 used in the production of paper toweling, bath tissue, or facial tissue are really quite delicate. Additionally, the rolls of web materials used in the production of paper toweling, bath tissue, or facial tissue typically have large cross-machine direction widths—typically in the order of 100 inches. When these thin, low basis weight, and large width web materials 18 are moved at typical manufacturing speeds (e.g., about 2,000 ft/min to about 4,000 ft/min) and at typical manufacturing web tensions (e.g., about 30 g/inch to about 120 g/inch), the web handling equipment used to manufacture these products (such as web material support 16) are designed to have low inertia.
Low inertial components are necessary to avoid breaking or otherwise damaging these otherwise delicate web materials 18. Designing low inertial equipment suitable for the above described converting operations requires that such equipment be manufactured from materials that have good mechanical (e.g., structural) strength and are light weight (i.e., low mass). Designing such low inertia equipment from traditional construction materials (such as steel) or from modern high-strength materials (such as carbon fiber), combined with the lengths of the equipment necessary to handle these high-width web materials results in web handling equipment having a high bend modulus (or bending moment).
One of skill in the art would understand that bending moment is the reaction induced in a structural element when an external force or moment is applied to the element causing the element to bend. The internal reaction loads in a cross-section of the web material support 16 can be resolved into a resultant force and a resultant couple. For equilibrium, the moment created by external forces (and external moments) are balanced by the coupling induced by any internal loads. This resultant internal coupling is called the bending moment.
Such is the typical case when a web material support 16 is caused to support a web material 18 having a low basis weight and large width, under high tension in a typical converting application. In principle, FIG. 3 shows a beam (here web material support 16) which is simply supported at both ends. In other words, each end of the web material support 16 can rotate but has little to no bending moment. This means that the ends of the web material support 16 only react to a shear load. As shown, when a wide web material 18 is subjected to an applied tension, T, it is not uncommon for a low inertia web material support 16 to deform in the manner of web material support 16′ in the direction of the applied tension, T. This is akin to a beam structural element that is subjected to a bending moment.
Additionally, the web material support 16 experiences deformation caused by the external load applied to the web material support 16 by the air moved within the wind tunnel 10 as it impacts the leading edge of the web material support 16. The deformation is generally caused by a strain or a stress field induced by the impact of air upon the low inertia device (e.g., web material support 16). In most cases, the deformations experienced by the web material support 16 can be elastic. This can cause erroneous measurements due to a changing deformation in the web material support 16 due to changes in the tension applied to the web material 18, the changing geometry of the web material support 16, or even changes in the velocity or volume of air impinging upon the leading edge of web material support 16. Additionally, deformations in the web material support 16 can cause variations in both the MD and CD length of the web material 18. In other words, a first portion of the web material 18 can have a displacement relative to an adjacent portion of the web material disposed in either of the MD, CD, or combinations thereof.
Thus, there is a need to provide a device for such web material test stands that provides laminar air flow at the leading edge of a web material support or at the point of attachment of the web material to a web material support. There is also a need to provide a device that can effectively reduce the deformation experienced by a web material support positioned within a wind tunnel. There is also a need to provide a device that can effectively reduce the deformation experienced by a web material disposed upon a web material test stand positioned within a wind tunnel.